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Weighting agents or heavyweight additives are used to increase slurry density for control of highly pressured wells. Weighting agents are normally required at densities greater than 17 lbm/gal where dispersants or silica is no longer effective. This is the most commonly used weighting agent. Hematite is a brick-red, naturally occurring mineral with a dull metallic luster. It contains approximately 70% iron.
A very small amount of goethite gives soil a yellow color and a very small amount of hematite gives soil a red color. These minerals are common in most soils and are abundant in highly weathered soils in the tropics. Both goethite and hematite have pH dependent charges. At high pH they have a negative charge and a cation exchange capacity. At low pH they have a positive charge and an an ion exchange capacity.
Abstract A recurring challenge in cementing concerns the effectiveness and the quality of cement blending and handling procedures. Some recent technologies involve dry-blending operations and cement-blend handling of specifically tuned blends that mix particles of different characteristics in terms of density, shape, size, and chemistry, including mineral and/or organic components. All blends are usually transported pneumatically, loaded to the rig, and then transferred to the rig silos. During the multiple transfers, depending on its characteristics, the blend may become difficult to flow and prone to segregation. This causes the blend to lose its homogeneity, and, consequently, it becomes difficult to use or even unusable. Flowability and robustness to segregation are essential blend properties for the handling process. Overall, the differences between particles in chemical nature, density, size, and shape will influence the flowability and the tendency to segregate. Dealing with blends is, therefore, complex since they contain small, medium, and coarse particles, all of them in various proportions depending on the targeted cementing-fluid density and set cement properties. To counter this challenge, an innovative methodology and equipment were systematically used in field cases to characterize the blend flowability and robustness to segregation. This new approach is used during the cement-job design as a preventive measure to validate the design and quality control of the dry-blending operations and transportation to the rig. This process helped in designing robust homogeneous blends, thus reducing the likelihood of blend transfer problems. Three case histories illustrate our new process. In the first case, we evaluated the blend selection between two designs that had good slurry performance for a critical job at a field location. We measured the shear under consolidation, the aerability, and the proneness to segregation of the two blends. Because both blends have good and equivalent flowing properties, we selected the blend that was less prone to segregation. In the second case, the field location designed four complex blends for lead and tail slurries having good slurry performance. We evaluated the shear under consolidation of the four blends, which were classified according to their flowability. Next, we measured the aerability of the blends as a second parameter to discriminate the blends, and then we considered segregation as the last screening parameter. In the last case, we used our flowability criteria to select the maximum acceptable concentration of an additive, which increased cement fluid performance but degraded blend handling. The outcome of this multidisciplinary approach of blend characterization helps the oil and gas industry anticipate blend-handling issues and continuously improve quality and field handling of engineered complex blends with high confidence and consistency.
Gadalla, Ahmed (Saudi Aramco) | Pino, Rafael (Saudi Aramco) | Ezi, Peter (Saudi Aramco) | Zayer, Nadeer (Saudi Aramco) | Hudaithi, Mohammad (Saudi Aramco) | Addagalla, Ajay (Baker Hughes) | Kosandar, Balraj (Baker Hughes) | Jadhav, Prakash (Baker Hughes) | Lawal, Ishaq (Baker Hughes) | Imran, Aqeel (Baker Hughes) | Hassan, Omran (Baker Hughes)
Abstract Drilling high pressure wells in the Khursaniyah field, Saudi Arabia, has become a challenge due to the high pressure flow from Base Jilh Dolomite formations coupled with loss circulation across the depleted Upper Jilh formations in the 8 3/8" section. The variations in formation pressure across these layers have led to issues like well flowing, losses, and stuck pipe causing considerable nonproductive time. This paper analyzes the historical problems encountered in the offset wells to identify the critical fluids related issues during drilling of this section: Thermal and pressure stability of fluids additives. Downhole pressure management. Differential sticking or induced losses. Low contamination tolerance to formation fluids influx. Barite sagging. Rheology and free-water management. This paper also discusses laboratory customization of optimized high-density fluid formulations and field handling guidelines to drill this critical 8 3/8" section and minimize fluid associated risks. The fluid was modeled to have as low a rheology and gelation profile as possible while suspending weight material by understanding the pressure envelope, bore-hole strength, torque, and drag constraints in combination with the fluid rheology and density relationship under the influence of anticipated drilling practices. The field application on this customized formulation with engineering observance was successful to drill this critical section and the case study for such well is presented in the paper.
Abstract Gas Migration through cement columns has been an industry challenge for many years. To control gas migration, high cement densities are required to successfully cement the high pressure formation. Formation gas/influx can migrate through the cement column resulting in gas being present at the surface. Current high density cement formulations do not provide good gas migration prevention due to settling and increase in permeability. To solve the settling problem and reduce permeability of cement, intensive lab work was conducted earlier by Al-Yami et al. (2009). The objective was to develop novel cement formula containing a combination of solids with different particle size distribution to minimize cement porosity and prevent solids settling. Compared to conventional high density cement weighted up with hematite, the developed cement showed no signs of settling, better fluid loss control and improved resistance against gas migration in the lab. Saudi ARAMCO has successfully trial tested their new developed cement formula (Gas Preventing Cement) in 5 wells in 2015 for 9 5/8" casings across high pressure formation to mitigate 9 5/8" X 13 3/8" Annular leaks. This is an effort to help in minimizing gas shut-in potential and safety risks due to casing-casing leaks. The new formula was applied with good cement returns to surface and good wellbore isolation according to the conducted well flowing test. In addition, loggings were run to ensure good bonding of cement. More high pressure gas wells will be cemented using this formulation.
Abstract Cementing a wellbore is a major stage in well completion and an initiation for production operations. One of the primary objectives of the cementing operations is zonal isolation. For effective zonal isolation and optimum hydrocarbon production during the life of the well, the entire drilling fluid, which presents in the annulus between the hole and the casing, should be removed. Over the years, several practices have been employed to help achieve mud removal and successful zonal isolation. From industry practices, efficient mud removal can be achieved with the use of spacers and flushes before cement is placed. The spacer system is designed according to different conditions including geological condition of the well. With the increasing tendency to drill high-pressure high-temperature wells, the design of robust and stable spacers is becoming more critical. Various spacer systems are available, but they may not be suitable for these conditions. The efficiency of spacer system is largely dependent on the rheological properties of the spacer at elevated temperatures. In this paper based on the laboratory investigations, the performance of specially designed spacer systems, their compatibility with mud systems and mud removal efficiency are compared in various temperatures. The spacers are weighted spacers, which are specially designed to meet the existed geological conditions of the well. The spacers contain a suitable surfactant package to increase its surface cleaning ability, a weighting agent (e.g. hematite) to adjust the spacer's density and a rheological modification agent. The proportions of these components in a spacer system will control the rheological properties of the final mixture, and thus, performance of the spacer. The spacers systems show a reliable performance in a wide temperature range.
Yan, L.L. (Drilling Research Institute, CNPC) | Wang, J.H. (Drilling Research Institute, CNPC) | Xu, X.G. (Drilling Research Institute, CNPC) | Feng, J. (Drilling Research Institute, CNPC) | Liang, H.J. (Tarim oilfield company,CNPC) | Xing, X.N. (Drilling Research Institute, CNPC)
Erosive and abrasive wear effect of water-based drilling fluid (WBM) on down-hole tools may reduce the service life of down-hole tools, and its magnetic contamination on Measurement-While-Drilling (MWD) directional tools may cause azimuth errors and reduce the wellbore position accuracy. The erosive and magnetic effects would be worse when a high density WBM densified with a high content weighting agent was employed. One of the main reasons of the erosive and magnetic effect is related to the weighting agent used. To reduce the erosive effect and magnetic interference of weighting agent, a micronized barite as a new weighting material was prepared in this paper, and then characterized by scanning electron microscope (SEM) and laser particle size analyzer. The prepared micronized barite, as a new weighting agent of high density WBM, has great promise to reduce the drag, erosion and magnetic interference along the horizontal section of large extended-reach wells and horizontal wells. It can also be used in HTHP wells and coiled tubing drilling technology. In our experiments, two conventionally weighting agents, barite and hematite were chosen to as the comparing samples. The erosive effects, magnetic contaminate tests, lubricity and rheological properties of high density WBM weighting with micronized barite, barite and hematite were evaluated on erosion instrument, a fluxgate magnetometer, an EP lubricity tester and a rotational viscosimeter, respectively. It was found that the high density WBM weighted with micronized barite showed less erosion, lower magnetic susceptibility, similar or better rheological properties, and smaller lubricating coefficient than that weighted with hematite or barite. Comparing with hematite or barite, the micronized barite could effectively reduce erosive wear on down-hole tools, reduce magnetic contamination on MWD directional tools, and control the rheological property of high density WBM, which would significantly contribute to the service life of down-hole tools, the wellbore position accuracy and the safety of drilling operations.
Tehrani, Ahmadi (M-I SWACO, a Schlumberger company) | Cliffe, Angelika (M-I SWACO, a Schlumberger company) | Hodder, Michael H. (M-I SWACO, a Schlumberger company) | Young, Steven (M-I SWACO, a Schlumberger company) | Lee, John (M-I SWACO, a Schlumberger company) | Stark, James (M-I SWACO, a Schlumberger company) | Seale, Suzanne (M-I SWACO, a Schlumberger company)
Abstract For many years, barite has been the standard weighting agent in the drilling fluid industry. Its high specific gravity has helped produce mud weights in excess of 19 lb/gal. Its hardness has rendered it easily millable to a particle size that reduces settling and minimizes losses on shaker screens and its adequate inertness has enabled it to be used in a wide range of drilling fluids containing different chemical components. Recently, however, dwindling supplies and increased consumption of premium barite have led to significant price increases across the world and a reduction in specific gravity in most commercial grades. This has led to renewed interest in alternative weight materials. Ilmenite and hematite are two minerals that have been used sporadically in the field. Compared to barite, their higher density impacts both the rheology of the fluids and the settling rate of the weight material. A known issue with these materials is their relatively high hardness, which can give rise to abrasion/erosion in the tubular and surface equipment. Another effect that has not been addressed sufficiently is the magnetic characteristic of these iron oxide-containing minerals which has the potential to affect the operation of direction drilling and some other downhole tools. There have been many studies on the use of ilmenite and hematite as weight agents for drilling fluids. These have dealt with the above issues individually or in a scattered manner. In this paper, we report the results of a comprehensive laboratory study on the application of ilmenite and hematite as weight materials for both water- and oil-based drilling fluids. The study includes the effects of different size grades of the materials on rheology and fluid loss, as well as dynamic and static sag. The paper will present relative abrasiveness of the materials compared to barite as measured by two different methods, and recommend size grades that can minimize the abrasion effects. The paper will also report the results of magnetic property measurements which impact operation of several downhole tools, and compares these with that of barite and several other minerals. To complete the comparative testing of these minerals, the results of heavy metal analysis will also be reported for each test mineral.
This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 163544, "Performance of Thermal Cements With Different Weighting Materials," by Jean-Philippe Caritey, SPE, and Jason Brady, SPE, Schlumberger, prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5-7 March. The paper has not been peer reviewed.
To maintain zonal isolation throughout the life of a high-pressure/high-temperature (HP/HT) well, the cement sheath must perform reliably at temperatures that can exceed 315°C. Weighting materials have largely been assumed to be inert with respect to set Portland cement; however, the present study reveals that this assumption may be false in HP/HT environments in which well temperature exceeds 260°C. Some weighting agents may react with the set Portland cement, causing strength loss and increased permeability. Fortunately, this effect can be prevented, and the set-cement integrity can be preserved.
Cement Blends. Five solid cement blends were prepared; their compositions are presented in Table 1. The blends were formulated according to the engineered-particle-size concept, wherein the volumes of coarse, medium, and fine particles are optimized to maximize the packing volume fraction (PVF). An increase in the PVF reduces the amount of mix fluid required to pre-pare a stable and pumpable slurry, and it increases the strength and reduces the permeability of the set cement.
The five blends contained 50% by volume of blend (BVOB) silica, which is sufficient to allow formation of the calcium silicate hydrate mineral xonotlite [Ca6Si6O17(OH)2] upon curing at temperatures above approximately 160°C. The weighting-agent concentration was held constant at 15% BVOB.
The slurries were prepared according to the recommended American Petroleum Institute (API) procedure.
Strength. The five slurries were placed in an ultrasonic cement analyzer (UCA) fitted with a dual-cylinder high-pressure pump that provided pulseless metering. They were cured at a final temperature and pressure of 302°C and 122 MPa, respectively, for periods of up to 100 days. Two additional tests were conducted at 274 and 288°C at a final pressure of 122 MPa.
It should be kept in mind that the UCA does not provide absolute strength values at such elevated temperatures because the transit time increases significantly during the heating period; therefore, one should consider strength trends vs. time. When possible, the cured- cement samples were crushed with a hydraulic press to obtain an accurate compressive strength. The recommended API procedure was followed.
Permeability. When possible, water-permeability measurements were per-formed on 5.08-cm-long, 2.54-cm-diameter cement cores with a liquid permeameter operating at a confining stress of 2.76 MPa.